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Marine Ecology Progress Series

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MEPS 465:53-67 (2012)  -  DOI:

Bioconversion of fatty acids at the basis of marine food webs: insights from a compound-specific stable isotope analysis

Marleen De Troch1,*, Pascal Boeckx2, Clio Cnudde1, Dirk Van Gansbeke1, Ann Vanreusel1, Magda Vincx1, Maria José Caramujo3

1Marine Biology, Krijgslaan 281/S8, and 2Laboratory of Applied Physical Chemistry (ISOFYS), Coupure Links 653, Ghent University, Gent 9000, Belgium
3Centre of Environmental Biology, Faculty of Sciences, University of Lisbon, Campo Grande C2, Lisbon 1749-016, Portugal

ABSTRACT: Polyunsaturated fatty acids (PUFA) are essential compounds that can limit the productivity of primary consumers in aquatic food webs, where the efficiency in energy transfer at the plant–animal interface has been related to food quality in terms of fatty acids (FA). At this interface, copepods play a pivotal role both as consumers of primary production and as a food source for higher trophic levels. Understanding the role of grazing copepods in the transfer of FA is therefore essential for our knowledge on the overall functioning of marine ecosystems. The harpacticoid copepod Microarthridion littorale grazed for 9 d on 13C labelled diatoms and bacteria in the laboratory and was then subjected to FA-specific stable isotope analysis. The objective of this analysis was to inspect the copepod’s ability to bioconvert short-chain FA (SC-PUFA, <20 carbons) into long-chain PUFA (LC-PUFA, ≥20 carbons) and the FA involved in the potential bioconversion pathways. Diatoms and bacteria were chosen as test diets because of their different FA composition, i.e. docosahexaenoic acid (DHA; 22:6ω3) was absent in the bacteria, and eicosapentaenoic acid (EPA; 20:5ω3) was <5% of the total FA weight of bacteria. The presence of labelled DHA in copepods feeding on bacteria showed that this PUFA must have been converted from other FA, possibly EPA. The FA composition of copepods in the laboratory was different from that of field copepods, which suggests the availability of more food sources in the field than those offered in the experiment. The weight proportion of C18 FA decreased in copepods feeding on either bacteria or diatoms relative to field copepods, while the proportion of both EPA and DHA increased. In contrast to planktonic calanoid copepods that have limited ability to bioconvert FA, benthic harpacticoid copepods apparently developed the ability to elongate FA and to exploit niches with poor quality food. Moreover, by improving the quality of the food they graze upon, especially in terms of EPA and DHA, harpacticoid copepods upgrade the nutritive value of food available to the higher trophic levels in marine food webs.

KEY WORDS: Fatty acids · Bioconversion · Harpacticoid copepods · Compound-specific stable isotope analysis

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Cite this article as: De Troch M, Boeckx P, Cnudde C, Van Gansbeke D, Vanreusel A, Vincx M, Caramujo MJ (2012) Bioconversion of fatty acids at the basis of marine food webs: insights from a compound-specific stable isotope analysis. Mar Ecol Prog Ser 465:53-67.

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